1. Technical Field
The present invention relates to a liquid crystal device which generates an electric field between two electrodes disposed on one substrate, and more particularly, to a liquid crystal device which can selectively perform a reflective type display and a transmissive type display. The present invention further provides an electronic apparatus having a structure including the liquid crystal device.
2. Related Art
Currently, liquid crystal devices (LCDs) are widely used in applications of electronic apparatuses, such as a cellular phone, a personal digital assistant (PDA), and a car navigation system. For example, the LCD is used as a displaying portion of an electronic apparatus, which displays a variety of information associated with the electronic apparatus in an image form. There are known a longitudinal electric field type LCD and a lateral electric field type LCD.
A representative longitudinal electric field type LCD is a twisted nematic type LCD (TN-type LCD) having a structure in which a liquid crystal layer is interposed between a pair of opposing substrates, the substrates are provided with corresponding electrodes, respectively, and a voltage is applied to the electrodes so as to generate an electric field acting in a direction perpendicular to the substrates. The longitudinal electric field type LCD controls the orientation of liquid crystal molecules in the liquid crystal layer using the longitudinal electric field, thereby modulating light passing through the liquid crystal layer.
On the other hand, the lateral electric field type LCD has a structure in which a liquid crystal layer is interposed between a pair of opposing substrates, two electrodes (a shared electrode and a pixel electrode) are disposed on either one of the substrates, and a voltage is applied to the two electrodes so as to generate an electric field (lateral electric field) acting in a direction parallel to the substrates or at an angle to the substrates. The lateral electric field type LCD controls the orientation of liquid crystal molecules in the liquid crystal layer using the lateral electric field, thereby modulating light passing through the liquid crystal layer.
In the lateral electric field type LCD, liquid crystal molecules are driven by the electric field acting in a direction parallel to or at an angle to the substrates. Accordingly, the orientation of the liquid crystal molecules is controlled within a plane which is almost parallel to the substrates, and thus a viewing angle to the liquid crystal molecules is not changed even if a viewing angle to the LCD is changed. As a result, the lateral electric field type LCD has a characteristic that a display performed based on the control of the orientation of the liquid crystal molecules can be viewed at a viewing angle in a wide range. This characteristic is termed “a viewing angle of an LCD is wide” or “an LCD has a wide viewing angle.”
As for the above-mentioned lateral electric field type LCD, a transflective LCD which can perform both a reflective type display and a transmissive type display is known. The transmissive type display is a display technique in which a display is performed using light passed through a liquid crystal layer one time and the reflective type display is a display technique in which a display is performed using light passed through the liquid crystal layer two times, that is, in this technique, light first passes the liquid crystal layer, is then reflected from a light reflective film, and finally passes the liquid crystal layer again. The transflective type display is a display technique in which the reflective type display and the transmissive type display are selectively performed. The transflective type LCD includes a reflective display region and a transmissive display region in one sub-pixel and shifts its operation modes from a reflective mode to a transmissive mode or from the transmissive mode to the reflective mode according to brightness of environment. By such a technique, the transflective type LCD can display a clear image even in a dark place at low power consumption.
Further in the transflective type LCD, optimum retardation values for the reflective display region and the transmissive display region are different from each other, and the liquid crystal layer is designed so as to have different layer thicknesses in the reflective display region and the transmissive display region. In greater detail, a layer thickness adjusting film is disposed in the reflective display region so that a layer thickness of the liquid crystal layer in the reflective display region is smaller than that of transmissive display region (Refer to JP-A-2005-338256).
In an LCD disclosed in JP-A-2005-338256 (Claims 6 to 7 and FIG. 2), a short edge of a layer thickness adjusting film, i.e. a boundary portion of a reflective display region and a transmissive display region, has a step plane. The step plane is an inclined plane which is naturally produced when the layer thickness adjusting film is patterned. An aligning force which aligns liquid crystal molecules becomes weak near the step plane and there is a probability that the alignment of the liquid crystal molecules is failed. In particular, in the lateral electric filed type LCD, liquid crystal molecules revolve in the plane parallel to the surface of the substrate when an electric field is generated by voltage application. After that, even after the electric field is extinguished, there is a probability that it is difficult for the liquid crystal molecules to recover their initial alignment state in the step plane where the aligning force is weak. As a result, the step plane, i.e. the boundary portion of the reflective display region and the transmissive display region, has failure in the alignment of liquid crystal molecules, resulting in decrease in display contrast. JP-A-2005-338256 explains the reason such that the relationship between the step plane and the direction of alignment processing are not adequately set.